Re: [Qemu-devel] [PATCH v2 13/17] vmdk: Implement .bdrv_co_pwritev() interface

[Pavel Butsykin]

On 29.04.2016 06:08, Fam Zheng wrote:
> On Thu, 04/28 15:16, Kevin Wolf wrote:
> > +typedef struct VmdkWriteCompressedCo {
> > +    BlockDriverState *bs;
> > +    int64_t sector_num;
> > +    const uint8_t *buf;
> > +    int nb_sectors;
> > +    int ret;
> > +} VmdkWriteCompressedCo;
> > +
> > +static void vmdk_co_write_compressed(void *opaque)
> > +{
> > +    VmdkWriteCompressedCo *co = opaque;
> > +    QEMUIOVector local_qiov;
> > +    uint64_t offset = co->sector_num * BDRV_SECTOR_SIZE;
> > +    uint64_t bytes = co->nb_sectors * BDRV_SECTOR_SIZE;
> > +
> > +    struct iovec iov = (struct iovec) {
> > +        .iov_base   = (uint8_t*) co->buf,
> > +        .iov_len    = bytes,
> > +    };
> > +    qemu_iovec_init_external(&local_qiov, &iov, 1);
> > +
> > +    co->ret = vmdk_pwritev(co->bs, offset, bytes, &local_qiov, false, false);
>
> Should it acquire s->lock?
The write_compressed callback is currently used only for image
converting, so I think the lock is not required.

> > +}
> > +
> >   static int vmdk_write_compressed(BlockDriverState *bs,
> >                                    int64_t sector_num,
> >                                    const uint8_t *buf,
> >                                    int nb_sectors)
> >   {
> >       BDRVVmdkState *s = bs->opaque;
> > +
> >       if (s->num_extents == 1 && s->extents[0].compressed) {
> > -        return vmdk_write(bs, sector_num, buf, nb_sectors, false, false);
> > +        Coroutine *co;
> > +        AioContext *aio_context = bdrv_get_aio_context(bs);
> > +        VmdkWriteCompressedCo data = {
> > +            .bs         = bs,
> > +            .sector_num = sector_num,
> > +            .buf        = buf,
> > +            .nb_sectors = nb_sectors,
> > +            .ret        = -EINPROGRESS,
> > +        };
> > +        co = qemu_coroutine_create(vmdk_co_write_compressed);
> > +        qemu_coroutine_enter(co, &data);
> > +        while (data.ret == -EINPROGRESS) {
> > +            aio_poll(aio_context, true);
> > +        }
> > +        return data.ret;
>
> Don't you have a plan to make the creation of coroutine for compressed write in
> in block layer?  Or will bdrv_co_pwritev gain a "compressed" flag
> (BDRV_REQ_COMPRESSED) in the future?
Actually, I already have these patches as part of the issue of backup
compression, hope to send today.

> Fam
>
> >       } else {
> >           return -ENOTSUP;
> >       }